Centripetal classifier



April 0, 1956 H. G. LYKKEN 2,741,366

CENTRIPETAL CLASSIFIER Filed Aug. 25, 1952 4 Sheets-Sheet l /4 //0 )J/A 3/ I J lg f7 GIN [V- EN TOR.

ENRY YKKE/V Fla. 1

ATTORNEYS April 0, 1956 H. 5. LYKKEN 2,741,366

CENTRIPETAL CLASSIFIER Filed Aug. 25, 1952 4 Sheets-Sheet 2 ML 90c IN VENTOR. f7EA/RY G LYKKE/V A 7- v-on/vz rs April 10, 1956 H. G. LYKKEN CENTRIPETAL CLASSIFIER 4 Sheets-Sheet 5 Filed Aug. 25, 1952 m m mm W m ufi M W G WM N E S April 10, 1956 H. e. LYKKEN CENTRIPETAL CLASSIFIER 4 Sheets-Sheet 4 Filed Aug. 25, 1952 Ha. 7/ 1 HQ. 75

INVENTOR. HENRY G. LYKKE/V mm #4 ATTORREYs United States atent CENTRIPETAL CLASSIFIER Henry G. Lykken, Minneapolis, Minn assignor to The Mieroeyclomat (30., Minneapolis, Minn, a corporation of Delaware Application August 25, 1952, Serial No. 396,126

ll) Claims. (Cl. 299-439) This invention relates to apparatus for classifying and/ or segregating pulverulent materials. In the production of finely divided solid material or powders, it is desirable, and in many cases essential that the material be classified on the basis of particle s ze so that the finished product will have in it particle sizes of only prescribed size ranges. Thus, in the milling of solid materials, the milling operation may produce a wide variety of particle sizes ranging from sizes which may be sieved, such as particles of a size in excess of fifty microns, down through the fine particle ranges, such as one to fifty microns and even ultrafine material below one micron. The separation of the relatively coarser materials of sieve sizes above fifty microns may be accomplished with comparative ease, but the separation of the ultrafines from fines, and particularly the production of narrow ranges of particle sizes, is exceedingly difficult. The difiiculty increases as the particle size decreases.

In centrifugal classifiers the airborne materials are rotated at a velocity required to throw the coarser materials radially outwardly and out of an anal flow. The oversize, as it strikes and rotates on confining walls, can be removed by various means. The fines remain in the air or other gaseous stream by which they are carried and are removed axially along with the gaseous stream, being thereafter subsequently collected as by means of a bag house, etc.

The so-called cyclone collector is in fact a centrifugal classifier designed to classify as between solid material and air. This it does only partially because a percentage of fine and superfine material remains in the air stream and goes out with the air. Other classifying apparatus has been proposed but they are subject to the difiiculty that in commercial applications they are unable to make a classification as between a wanted particle size, such as two microns, and an unwanted particle size, such as three microns. In such prior apparatus a large percentage of the wanted smaller sizes will be thrown out with the undesired oversize, and conversely, particles only slightly larger than the wanted size are frequently collected with the smaller wanted size.

In the centripetal type classifier, the classifying action is reversed. The airborne material enters the classifying chamber peripherally in contact with the wall, at which point, the oversize remains, while the finer and wanted particles are drawn inwardly with the air into a high speed axial rotor assembly connected to a suction fan, from which fiow they are discharged to the collecting system. Therefore, in the centripetal classifier the oversize is not thrown radially outwardly from a theoretical axial flow by centrifugal action, but rather the fines are drawn radially inwardly from a peripheral flow on the chamber Wall against centrifugal action and induced by the centripetal drag of the air flow. The oversize remains on the wall, from where it may by mass action, drop back into the grinding zone of the mill with which the classifier is used, orbe otherwise discharged.

"ice

The centripetal classifier is preferably of the vertical axis type, but may also be constructed on a horizontal axis. It is preferably constructed as a multiple deck unit with a relatively high classifier zone and having ample classifying area. i

The present invention is a continuation-in-part of my co-pending application Serial No. 278,239, filed March 24, 1952.

It is therefore an object of the present invention to provide an improved centripetal classifier capable of providing precise classification of particle size.

It is a further object of the invention to provide an improved centripetal classifier capable of providing on a commercial scale, precise classifications of materials in the fine and ultrafine ranges.

It is another object of the invention to provide a classifier apparatus which admits of complete recovery of a desired particle size from the milI load and is capable of providing a precise classification on a particle size basis, even in ranges below one micron, such as a separation of particles of minus one micron size.

It is a further object of the invention to provide a classitying apparatus which is relatively independent of rotative speed, except as is required to maintain ample centrifugal stresses.

It is a further object of the invention to provide an improved classifier wherein the classifier unit may be assembled and disassembled and revised and re-arranged readily without enfire redesign or reconstruction of the unit, so as to permit adaptation of the particular generalized classifier designs to the specific requirements of particular materials and sizes of materials.

It is another object of the invention to provide an improved classifier of large capacity capable of being extended axially to provide exceedingly large capacities, while at the same time maintaining uniformity of classification throughout the axial length of the classifier.

It is another object of the invention to provide a simplified classifier construction and design of exceedingly rugged construction, capable of being assembled from standardized parts and with relatively little machining.

It is a further object of the invention to provide an improved classifier of improved design and capable of very high rotative speeds.

Other and further objects of the invention are those inherent in the apparatus herein illustrated, described and claimed.

The invention is illustrated with reference to the drawings in which corresponding numerals refer to the same parts and in which:

Figure 1 is a vertical sectional view through a combined mill and classifier embodying the invention herein;

Figure 2 is a fragmentary horizontal sectional view taken along the line and in the direction of arrows 22 of Figure 1;

Figure 3 is a fragmentary vertical sectional view of a portion of a mill, and integral classifier of slightly modified form;

Figure 4 is a fragmentary sectional view taken along the line and in the direction of arrows 4-4 of Figure 3;

Figure 5 is a fragmentary much enlarged horizontal sectional view of a portion of the apparatus shown in Figures 3 and 4;

Figure 6 is another slightly modified form of classifier in accordance with the present invention, this figure being a vertical sectional view of a portion of the mill and an integral classifier unit;

Figures 7a and 7b are fragmentary horizontal sectional views showing several forms of classifier blading. These views correspond to sections taken along the line and in the direction of arrows 77 of Figure 6.

' Referring to Figures 1 and 2 of drawings, the classifier is shown combined with a rotary the accompanying mill. It is to be understood, however, that a rotary mill need not be combined with a classifier, and that the classifier can be used' as a separate unit. .However, when so combined, the classifier is preferably positione'd over or' will be understood'that the combined mill and classifier herein illustrated are merely exemplary. Referring to Figuresl and 2' there is illustrated an exemplary form in which the classifier is above the mill, although other arrangements can be had. As shown, the unit includes a base generally designated having a top portion 11 upon which'the bearing structure generally designated 12 is attached by means of a ring 13 that is in turn held in place by the bolts 14-14. Upon the base 11 there ismounted the mill structure shown generally opposite the bracket 15. The mill structure has a cylindrical outer casing16.

having a lower flange at 17 attached to the base by the bolts 1818. 'At the upper end of the mill structure 7 there is aflange 19 which is welded or otherwise attached to the ring plate 20. The classifier unit is that portion of the apparatus above the plate 20 and includes a cylindrical shell 21 which may be of larger diameter than the mill 16. The cylinder 21 terminates at the ring plate 22 to which there is attached by means of bolts 23 the lower flange 24 of a larger cylindrical scroll 25 having the flange cover plate 27 serves to support the upper bearing assembly generally designated 28. The bearings 12 and 28 are within the province of mechanical engineering design and i V will not be further described otherthan to say that they are adequate for the rotative speeds and loads involved and preferably are ball or roller bearing, dust sealed and lubricated for the life of the machine. The two bearings 12 and 23 serve to support the shaft generally designated 30. At the lower end of the shaft there is provided a multiple V-belt or other drive pulley 31.npon which the belt generally shown by the dotted lines 31A are adapted to run. The housing 1011 is provided with a window openingat 32 for easy servicing of the belts.

' the clamping ring 37 and screws 38, so as to provide any smaller size aperture 39, up to the size of aperture for regulating the in-flow of air 'or other gas into the mill. The shaft30 is provided at its lower end with a collar 49 against which the lower hub 41 of the assembly is pressed. The lower hub 41 carries the fan plate'42 having the fan blades 43 and also carries the lower stage of the mill, of which a fragmentary portion is shown opposite the bracket 44. Thelrnill may have a pluralityof stages and between each stage there are preferably pro vided vibratoryplates as at 45 according to the aforesaid application of Joseph Lecher, Serial No. 242,390. The

' upper grinding stage of the mill, as shown opposite the bracket 48, is enclosed at its top by the vibratory plate 49. A liner of wear resistant material may be provided in the mill at 59. The gaseous fiowthroughthe mill is in a general direction axially from bottom to top and emerges through the annular space 52 around the periphery of the plate49 and between the plate 49 and the liner 50. The gaseous flow through the mill carries the milled products into the classifier sectionshown above the ,plate 20. Above the spacer 54 there is mounted a plate 55 which 26 upon which there is attached the cover plate 27. The

4 a r forms the lowermost rotative part of the classifier structure. In the form of classifier shown in Figures 1 and 2 a plate 55 is surmounted by a smaller diameter plate at 56 and upon this is mounted a frusto-conical member 57 upon which thecylindrical member 58 is in turn mounted. The cylindrical member 58 is surmounted by the fan plate 59 having the fan blade 69 and is clamped in place by the ring nut 61 which bears upon the spacer washer 62. In this way the entire assembly is held tightly clamped between the nut 61 and the flange 4% on the shaft.

The fan plate 59 carrying the blades 69 seats upon a' closure ring at 65 which'is welded to.a cylindrical shell at 66, the shell in turn bearing upon a minor ring 67 which may, if desired, be provided with very small fan blading at 68, as will be described. Between the plates '67 and 55 there is mounted the essential classifying struc- The' classifier is composed, as shown in Figure 2,

ture. of a plurality of radial blades 70 of identical pattern. Each of the blades has a maximum vertical dimension between the lines 71 and 72 and is notched out at the top, to the level of line 73 and is notched out at the bottom to the level of the lines 7 4. The notches in the blades'are provided to receive the ring 75 at the top and 76 at the bottom and the surfaces 77 on the upper notchand 78 on the lower notch therefore rest against the inner surfaces of the rings 75 and 76, respectively. The rings accordingly act as hoops against which the radial blades are thrown and by which they are held during the rotation of the mill. The inner surface 79 of the blade rests against.

the outer surface of the ring St) at its upper end and against .the outer edge of the plate 56 at its lower end. The radial.

blades are accordingly locked against movement either radially inward or radially outward by the assembly as shown. The ring 80 is preferably attached by welding to the plates 67. The blades are held in radial position by notches in rings 81,- 82, 83 and 84, the rings being mortised back as far as the surfaces 81A, 82A etc. 'The radial blades are themselves mortised along the inner surface 79 to receive the rings 81--84 and accordingly the radial blades 70 support the rings Lib-84 in vertically (axially) spaced relationship, and the rings 81-84 in turn' hold the radial blades in radially spaced relationship. It will be understood that each of the rings 8184 has an outer diameter flush with the outer edges 70A of the radial blades. In addition to the notches in the radial blades 70 receiving the rings 8184, there are provided additional notches which receive the outer thin edge A of the weir rings 90. The weir rings 90 are of identicaldesign and have an inner diameter flush with.

the inner diameter of the rings 81-84, and the weir rings 90 have a maximum thickness at such inner diameter.

The weir rings are then gradually reduced in thickness to the point 90B and outwardly therefrom the weir rings preferably have a uniform thickness until the edge 90C is reached, at which place the edge is sharpened off to a of the weir rings 90 and rings 8184.. The radial blades 7 are then driven in radially until a unit latticed structure having a generallycylindrical outer surface is provided. This unit-structure can then be lowered axially 'so as to bring the lower portion of the radial blades as tongues into the space between the outer edge of the plate 56 and the inner surfacev 78 of the ring 76. The ring 75 is then lowered into place and it is followed by the plate 67, which carries .the ring 80. Thereafter, it is only necessary to put on the structure between plates 22+27. It willbe noted that the ring 22 is provided with one or more open ings 92 around its periphery, each of the openings being In assembling the structure, the weir provided with a slide case 92A sons to permit more or less of the opening to be uncovered. Within the cylindrical shell 25 there is provided a spacer 93 upon which the ring 94 rests and this ring in turn supports the cylindrical wall 95 which then supports the inwardly projecting ring 96. A ring 97 is removably detached by means of screws 98 to the upper surface of the plate 22. The rings 96 and 97 accordingly project into the space between the plates 67 and the plates 65, but the inner edges 96A and 97A which may be sharpened as at 96A or square as at 97A are spaced from the outer surface of the cylinder 66. The openings 92 permit fresh air to flow as shown by arrow 99 into the space between the plates 96 and 97, which do not rotate, and a small amount of this air is drawn into the space between the upper surface of the plate 96 and the lower surface of the plate 65, as shown by the arrow 100. A somewhat larger quantity of this air is moved as shown by the arrow 101, by the fan blading 68, Where used, and is projected back as indicated by the arrow 102 into the space within the classifier chamber, between the inner surface of the shell 21 and the outer surface of the combined rotating unit. This construction allowing the air flow as described is in accordance with the co-pending application of myself and Tibor Rozsa, Serial No. 311,714, filed September 26, 1952.

Upon the wall 21 of the classifier section there may be provided one or more skimmer units 194 constructed in accordance with my application Serial No. 278,239, filed March 24, 1952.

During operation a mixture of coarse and fine particles moves upwardly through the space 52 as shown by the arrow 1155 and the flow is then set into turbulence by the radial blades '76. The rotation of the entire mill and classifier rotary unit causes swirls of solid material, carried by the gaseous fluid within the mill and classifier to be set up in the spaces between the radial blades 7t57t3 and the solid particles in the gaseous fluid thus whirling in the spaces between the radial blades is subjected to heavy centrifugal force especially at the periphery of the rotor unit, and the larger and heavier particles are propelled outwardly with greater effect than the smaller particles which are more susceptible to the action of the gaseous fluid about them. The weir rings 999l provide communicating passageways 166 between their portions 99A and the adjacent surfaces of the rings 3184 and accordingly at the edges of the weir rings 91 there is a prescribed and controllable inward velocity of air or other gaseous fluid in the classifier, which is determined in part by the communicating passageways 1% and in part by the metering communicating passageways 1ti71t i between the inner thickened portion of the weir ring and the plates 8134. It will be noted that the frustoconical shape of the inner member 57 allows a uniform velocity in the axial passageway between its outer surface and the inner surfaces formed by the combined spaced weir rings 99 and rings 31-84. Accordingly, each of the communicating passageways between each weir ring and the adjacent rings 8084 and plate 56 is subjected to the same uniform pressure differential and accordingly through each of the spaces 1%7-167 there is a uniform and controlled velocit fiow. This flow is combined as indicated by the arrow 198 and is moved outwardly as shown by the arrow 109 through the fan blading 6tl n3. A suitable outlet 110 in the shell 235 permits the thus separat d and graded ultrafine particles, or line particles, depen ing upon the constants of the classifier, to be removed and separated. By varying the amount of draft produced by the fan blading 613, and by varying the dimensions of the weir rings so as to vary the communicating passageways 107, the very accurate control of flow may be achieved.

Referring to Figures 3, 4 and 5, the structure is similar except that the radial blades 12ti120 are curved inwardly at their inner ends and are anchored to through pins or rods 122 that in turn extend through holes in the upper 6 ring 123, the intermediate rings 124-124 and the lower plates 125 and 126. The through pins are welded to the plates 125-426 and to the rings 123-124. The radial blades, which are notched to fit the assembly, as described with reference to Figures 1 and 2, are then set in place and are welded between each communicating passageway 128-132 to the rods 122. It is preferable that the welding be accomplished toward the front of the rod as well as toward the rear of the rod so as to minimize any tendency of the blade to unwrap from the rod by twisting. The welding is thus best applied at 133 and 134. In addition, it is preferable to weld in the inner tips of the blades to the adjacent rings 123-124 and plate 125 upper and lower as shown at 135. In this way an exceedingly rugged structure capable of withstanding the forces induced by exceedingly high rotative speeds, is accomplished. In this form of the invention also, the upper cylindrical member 58 is provided with keyways at 136 into which a plurality of plates 13? may be set for stabilizing the position of ring 66.

In this form of the invention a space is provided at 1dii14ti between each of the rods 122-422 and the adjacent surface 12t3A-120A of the inner tip of the radial blade next adjacent. By varying the diameter of the rods 122 or the thickness of the radial blades 126 or the number of radial blades and rods for a given diameter of classifier, the dimensions of the spaces 140 can thereby very easily be controlled for in effect forming a metering screen or grid through which air flow proceeds as indicated by the arrows 141. In this way the velocity of flow for any given classifier may easily be varied without varying the overall form of the classifier.

Referring to Figures 6, 7A and 73 there is illustrated another slightly modified form of classifying unit in which the radial blades may be set in straight radial position, as shown by the Figure 7A or tipped forwardly or rearwardly, as shown by the Figure 7B. In this form of the invention also the weir rings i l- 9 of the form shown in Figures 1 and 2 and the weir forming rods 122 of Figures 3, 4 and 5 are replaced by a cylindrical screen generally designated 15%. This screen is simply set against the surface formed by the inner edges of the rings 8184. The screen may easily be replaced and varied for providing different screen openings and hence different velocities of flow radially inwardly in the spaces between the radial blades 151. Thus, the screen 15% may be of woven wire or may be of metal, having holes punched or pertused therethrough, thereby afiording a means for readily varying the velocity of gaseous inflow through the classifier. This facility enables the ready selection of velocities when Working with difficult problems of particle size separation, particularly for exploration and analysis of size separation problems, with reference to specifying classifiers for particular materials.

In operation of this classifying device, therefore, the individual rotor units act as reverse flow radial blade fans. The high static pressure of the mill fans which in this case are connected to the classifying units provide for this reverse flow. The particles therefore are circulated in a suspension in the annular zone between the rotor and the casing wall 21, the larger particles generally in a zone nearer the wall while the fines and near fines are generally nearer the rotor, and are from there sucked nto the rotor unit and carried out of the unit in the direction of the arrows 163 and 1119.

In order to illustrate this action, let us assume that there is no air flow through the system and that there is some pulveruient material present. In this case, the rotation of the rotor unit establishes a turbulence within the system and air and material is drawn radially inwardly along the receding face of each radial blade, and is discharged outwardly along the forward side of the next succeeding blade, in a constant recirculation at high speed. The air with its load of fines and near fines is drawn in wardly by the partial vacuum created on the receding face 'of'ea ch blade, and by the partialvacuum created at the center of the rotor. In other words, the flow moves inwardly to the heel or bottom of the blade where it reverses its course and goes out along the forward surface of the next succeeding blade.

The initial flow of material into the rotor unit is a quently the larger particles are constantly held outside.

of the rotor unit. 'These larger particles are'preferably removed from the classifier chamber by any suitable extraction means, for example, the skimmer unit 104.

, Another classification of particles isaccomplishcd within the confines of the rotor unit, and additional variables, such as flow or" air, length of blading, and number .of radial blades must be considered. Most of the air, if not all, entering the unit moves inwardly to the heel or bottom of the radial blade before reversing its course, however, this' is not true in the case of the solid material. The individual solid particles are spun out of the inwardly directed air stream and into the outgoing air stream in a progressive manner according to the size and mass of the individual particle. Thus, for a given rotative velocity, blade spacing and length or" blading, material of a constant density finer than, for example, 100 microns, may enter the rotor unit, but only that material finer than one micron will reach the bottom of heel of the blading, the remainder being centrifugally disposed of along the way. Furthermore, in accordance with the example above given, if the rotative velocity is increased, or if the numher or length of the blades is increased, only material of sub-micron size will be able to reach the bottom of the unit. Conversely, if any of the above mentioned factors are diminished, particles substantially in excess of one micron will reach the bottom of the rotor unit.

The inwardly moving air flow is superimposed on the rotating unit in order that it will carry out material which 1 reaches the bottom of the unit. When'no air is passed through the unit, the solid particles therein are classified over and over, and as the air reverses its path, the material is carried along with hand out of the rotor unit.

, Therefore/to effect a flow of material through the unit,

the suction at the point of reversal must be somewhat in excess'of the force produced by the classifier blades so that the increased incoming air can be continuously withdrawn, while still allowing the normal amount to recirculate in the blading. larger particles will be removed from the unit, because the increasing velocity will depress the point where the successive particle sizes are spun off into the outflow, consequently providing a greater area for selection of particles for the outflow. It is now clear that the rate of product withdrawal is'only a portion of the rate of inflow from the turbulent zone. lt is this factor which allows the apparatus of my present invention to produce such a sharp classification between various particles having a very close size range. In order to have a constant and uniform rate of delivery from the rotor unit to the delivery port, a pressure differential of from one to two inches of water should be provided therebetween.

The classifying device of my present invention can be designed as to number of decks, capacity per deck blade spacing and number of blades, etc. to meet specific re-,

quirements. as to particle size and character of material, for example; density and particle size desired. Superfine classification of material of low specific gravity requires very large areas of classification.

When the air flow is increased,

As many apparentlywidely. different embodiments of this invention may be made without de'parting fr'omthe spirit and scope thereof, it is to be understood'that I'do not limit myself to the specific embodiments herein;

What'iclaimis: 1

1. An apparatus for classifying pulverulent solids of mixed particle size comprising a cylindrical shell having an opening inorie end for'introducing a gaseous flow havingthe solid particles of mixed sizes therein, a rotary unit axially within said cylindrical shell, said rotary unit having at least one axial passageway thereimsaid rotary unit extending longitudinally beyond said shell, means outside the shell for inducing a gaseous flow through said axial passageway, communicating radial passageways from 7 said axial passageway to the periphery of said rotary unit, said communicating passageways being defined by a plurality of radially spaced blades and annular rings spaced longitudinally of the rotary unit, said axial passageway being gradually tapered in the axial direction.

2. The apparatus as in claim 1 further characterized V in that said communicating radial passageways have metering spaces of predetermined area therein.

3. The apparatusof claim 1 further characterized in that. a screen is provided across said communicating passageways. 'Y

4. The apparatus of claim 1 further characterized in that the radial blades and spaced annular rings of'said rotary unit are held together by axial rods spaced between the inner surfaces of the radial blades and forming spaces with surfaces of adjacent radial blades, said blades being attached to said rods.

5. A classifier comprising a cylindrical'shell having an inlet opening at one end and an annular axial outlet opening at the opposite end, a classifier rotor within such .having radial notches therein seated in said mortises and supported solely by said radial blades, and wier rings having edges fitting into the spaced mortises of said radial blades for supporting said wier rings in longitudinally spaced position between successive spaced annular rings, said rotor. including at least one longitudinal passage of gradually increasing cross-sectional dimension toward said outlet end in communication with the radial passageways defined by said spaced annular rings, and a fan on said rotor structure for inducing a flow of gaseous fluid into the rotor, between said radial and spaced annular rings,.

thence longitudinally of the rotor to the exterior ofsaid classifier shell. 7

6. The apparatus of claim 5 being further characterized in that said wier rings are gradually thickened in a radially inward direction.

7. An improved classifier comprising a cylindrical hous- 7 ing, having end closure plates, an inlet opening. through one end plate and an annular outlet opening co-axial-with the cylinder through the other end plate, a classifier rotor journaled for rotation in said housing, said rotor including a pair of spaced plates, blade retaining rings mounted between said plates, one ring being against each of said plates, a plurality of radiallyspaced blades on the rotor, each of said blades having an extending tongue at each end thereof, said tongues extending against the spaced plates and against the inner edge of said rings so as to be held thereby, each of said radial blades being provided 7 with axially spaced notches along the radially inner edge thereof, a plurality of rings having radial notches therein,

Ola.

each of the radial blades having additional notches evenly spaced between the first mentioned notches, and wier rings having outer edge portions received in said additional notches so as to be supported thereby, said wier rings extending radially inwardly of said radial blades and terminating adjacent the radially inner edges of said rings, said rotor including at least one longitudinal passage axially thereof from that portion of the rotor between the plates and thence outwardly through the outlet of the housing, a supplementary housing outside the first housing and fan blading on the extending portion of said rotor and in said supplementary housing for inducing a flow of gaseous fluid into the rotor between said rings and radial blades and past said wier rings and thence through said longitudinal passage to said supplemental housing, said supplemental housing having an outlet.

8. The apparatus of claim 7 being further characterized in that said wier rings are gradually thickened in a radially inward direction.

9. A classifier comprising a cylindrical housing having end closure plates, one of said end closure plates being provided with an axial annular inlet opening and the other end plate being provided with a smaller axial annular outlet opening, a rotor extending axially through said cylindrical housing outlet opening and iournalled for rotation therein, said rotor including a plurality of radially spaced blades and axially spaced rings; said blades and rings being fitted together to form a latticed cylindrical structure, a fan assembly mounted on said rotor, and a supplementary housing around said fan housing and attached to said cylindrical housing, said supplementary housing having an outlet opening therein.

10. An improved classifier comprising a cylindrical housing having closure plates at opposite ends thereof,

an annular inlet opening through one of said closure plates and a smaller annular outlet opening through the other of said closure plates, a rotor shaft journaled for rotation within said housing, a rotor structure in said housing comprising a plurality of radially spaced blades and axially spaced rings mortised together to form a latticed cylindrical structure, said rotor structure being mounted on said shaft for rotation therewith, said rotor structure including a passage longitudinally thereof extending through the outlet opening, a screen on said rotor structure between said assembly of radial blades and rings and said longitudinal passageway, and fan blading on said rotor on that portion of the rotor extending outside the cylindrical housing for inducing a flow of gaseous fluid through the rotor structure between said radially spaced blades and the axially spaced rings, and then through said screen and longitudinal passage, and a supplementary fan housing attached to the cylindrical casing enclosing said fan, said supplementary fan housing having an outlet opening therein.

References Cited in the file of this patent UNITED STATES PATENTS 1,933,606 Sturtevant Nov. 7, 1933 2,206,981 Sturtevant July 9, 1940 2,269,412 Sturtevant Jan. 6, 1942 2,294,921 Lykken Sept. 8, 1942 2,304,264 Lykken Dec. 8, 1942 2,350,737 Eiben June 6, 1944 FOREIGN PATENTS 535,314 Germany Oct. 8, 1931 816,051 Germany Dec. 20, 1951 

1. AN APPARATUS FOR CLASSIFYING PULVERULENT SOLIDS OF MIXED PARTICLE SIZE COMPRISING A CYLINDRICAL SHELL HAVING AN OPENING IN ONE END FOR INTRODUCING A GASEOUS FLOW HAVING THE SOLID PARTICLES OF MIXED SIZES THEREIN, A ROTARY UNIT AXIALLY WITHIN SAID CYLINDRICAL SHELL, SAID ROTARY UNIT HAVING AT LEAST ONE AXIAL PASSAGEWAY THEREIN, SAID ROTARY UNIT EXTENDING LONGITUDINALLY BEYOND SAID SHELL, MEANS OUTSIDE THE SHELL FOR INDUCING A GASEOUS FLOW THROUGH SAID AXIAL PASSAGEWAY, COMMUNICATING RADIAL PASSAGEWAYS FROM SAID AXIAL PASSAGEWAY TO THE PERIPHERY OF SAID ROTARY UNIT, SAID COMMUNICATING PASSAGEWAYS BEING DEFINED BY A PLURALITY OF RADIALLY SPACED BLADES AND ANNULAR RINGS SPACED 